A 21 year old male soccer player presents with left side groin pain. He reports feeling a pull during a tackle, in a match that he played 2 weeks ago. He continued to play and practise since the incident, and the pain hasn't subsided. He is able to weight bear and run, but sudden twisting movements aggravate the pain. He has a history of low back pain. Coughing, sneezing or holding his breath doesn't worsen his symptoms. On examination, his active ROM was limited by discomfort, but passive ROM was full. No inflammation visible. Manual muscle tests showed weakness on the left adductor. A groin strain would typically involve which muscle?